Commonly used concentration expression methods in analytical chemistry

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This post was last edited by qugd on 2010-6-28 18:00 When expressing the results of analytical chemistry, different units of expression will be used. These units of expression should be used in a convenient way in practical applications. molarity, molar concentration, the ratio of moles of solute to solution volume, represented by M ； This is the most commonly used method of expressing concentration and is also the current international standard unit. ； formality, apparent concentration, formal concentration, the total concentration of solute in the solution, regardless of the chemical form of the solute, represented by F ； This may be rarely encountered in practical applications, but it is actually common, such as TOC concentration, VOC concentration, total iron concentration, etc. ； Normality, equivalent concentration, is a concentration expression that was very commonly used and very practical in the past. The equivalent number of solute is compared to the volume of the solution, represented by N. ； This concentration is very convenient when calculating redox reactions ； molality, molar concentration, the ratio of moles of solute to the total weight of the solution, represented by m ； This is the unit used when calculating solute activity. For dilute aqueous solutions, M is approximately equal to m. ； Weight%, weight percentage concentration, this is easy to understand, it is the number of grams of solute contained in 100 grams of solution, expressed in %w/w ； Volume%, volume percentage concentration, is also easy to understand. It is the number of milliliters of solute contained in 100 milliliters of solution, expressed in %v/v ； Weight-to-volume%, weight-to-volume percentage, is also easy to understand, it is the number of grams of solute contained in 100 grams of solution, expressed in %w/v ； The above units are reversed, volume weight percentage, no one seems to use it. Parts per million, one part per million, that is, the number of parts of a solute in one million parts of a solution, dimensionless, expressed in ppm ； parts per billion, one part per billion, that is, the number of parts of a solute in a billion parts of a solution, dimensionless, expressed in ppb.